Self-Canceling Magnetic Structures

ABSTRACT

A structure comprises a plurality of first turns of a coil and a plurality of second turns of the coil having a similar shape as the plurality of first turns of the coil, wherein the plurality of first turns of the coil and the plurality of second turns of the coil have a similar center position and a current flowing through the plurality of first turns of the coil and a current flowing through the plurality of second turns of the coil are in opposite directions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims priority to, U.S. ProvisionalApplication No. 62/307,915, titled, “Self-Canceling Magnetic Structures”filed on Mar. 14, 2016, which is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to a coil structure, and, in particularembodiments, to a coil structure in a wireless power transfer system.

BACKGROUND

Many power inductors, including those used in power converters and EMIfilters, and transmitter coils and receiver coils in wireless powertransfer (WPT) systems, are required to operate at high frequencies in arange from 10 KHz to few hundreds of MHz. To achieve better efficiency,the windings of such inductors are required to be carefully designed.Since magnetic materials' performance at such a higher frequency is notgood or a significant magnetic field is need in a given space such asthe space required in a WPT system, air core inductors are commonlyemployed.

One drawback of an air core inductor is it may cause significantmagnetic interference to nearby components. More particularly, byemploying the air core inductors, the interference between the air coreinductors and the surrounding components can cause significant issuessuch as disturbing the operation and/or damaging the surroundingcomponents, increasing power losses caused by induced eddy currents inthe adjacent metal components, and/or the like.

FIG. 1 illustrates an implementation of a conventional coil structure.FIG. 1 shows a coil structure having two turns. These two turns 102 and104 can be implemented as either wires or traces on a printed circuitboard (PCB). As shown in FIG. 1, the first turn 102 starts from a firstterminal of the coil structure 100 and ends at the starting point of thesecond turn 104. The second turn 104 ends at a second terminal of thecoil structure 100. As shown in FIG. 1, the first turn 102 and thesecond turn 104 of the coil structure 100 are implemented as twoconcentric circles. The currents of these two concentric circles flow ina same direction as shown in FIG. 1. The coil structure 100 can be ofother suitable shapes such as oval, rectangular and the like.

The coil structure 100 shown in FIG. 1 can provide the desiredinductance of a wireless power transfer system. However, a significantportion of the magnetic field of the structure may expand out of thecoil structure 100.

FIG. 2 illustrates a magnetic flux distribution of the coil structureshown in FIG. 1. The horizontal axis of FIG. 2 represents the distancefrom the center of the circles shown in FIG. 1. The unit of thehorizontal axis is meter. The vertical axis represents the flux densityof the magnetic field generated by the coil structure shown in FIG. 1.The unit of the vertical axis is Tesla. The flux density of the magneticfield is measured at a height of about 1 mm above the top surface of thecoil structure 100 shown in FIG. 1. The flux density shown in FIG. 2 istaken along line A-A′ shown in FIG. 1.

As shown in FIG. 2, the flux density has two positive peaks 112 and 116,and two negative peaks 114 and 118. Referring back to FIG. 1, the twoturns of the coil structure 100 are immediately next to each other. Inaddition, the currents flowing through the two turns are in the samedirection.

As shown in FIG. 2, slightly away from the peaks of the flux density,the magnetic field generated by the currents flowing through the twoturns is not canceled out. As a result, the magnetic flux density inFIG. 2 takes a longer distance to decay to a lower value.

FIG. 3 illustrates another magnetic flux distribution of the coilstructure shown in FIG. 1. The horizontal axis of FIG. 3 represents thedistance from the center of the circles shown in FIG. 1. The unit of thehorizontal axis is meter. The vertical axis represents the flux densityof the magnetic field generated by the coil structure shown in FIG. 1.The unit of the vertical axis is Tesla. The flux density of the magneticfield is measured at a height of about 10 mm above the top surface ofthe coil structure 100. The flux density shown in FIG. 3 is taken alongline A-A′ shown in FIG. 1.

The magnetic flux distribution shown in FIG. 3 is similar to that shownin FIG. 2 except that the flux density of the magnetic field is measuredat a height of about 10 mm rather than 1 mm above the top surface of thecoil structure shown in FIG. 1.

As shown in FIGS. 2-3, since the magnetic flux density takes a longerdistance to decay to a lower value, a significant amount of the magneticflux generated from the coil structure 100 shown in FIG. 1 is outsidethe coil structure 100. This magnetic field may cut into nearbyconductive components, thereby generating power losses and causinginterference. Especially, if the coil structure 100 is a WPT coil andanother component is a Near Field Communication (NFC) tag. When the NFCtag moves adjacent to the coil structure 100, the components in the NFCtag may be disturbed or damaged by the magnetic field generated by thecoil structure 100. It is therefore important to have a coil structurewith minimized impact on nearby components.

SUMMARY

In particular embodiments, a coil structure may have less magneticinterference with a nearby component in comparison with a conventionalcoil structure.

In accordance with an embodiment, a structure comprises a plurality offirst turns of a coil and a plurality of second turns of the coil havinga similar shape as the plurality of first turns of the coil, wherein theplurality of first turns of the coil and the plurality of second turnsof the coil have a similar center position and a current flowing throughthe plurality of first turns of the coil and a current flowing throughthe plurality of second turns of the coil are in opposite directions.

In accordance with another embodiment, a system comprises a first coilhaving a first winding structure comprising a plurality of first turnsand a plurality of second turns of the first coil having a similarshape, wherein the plurality of first turns and the plurality of secondturns have a similar center position and a current flowing through theplurality of first turns and a current flowing through the plurality ofsecond turns are in opposite directions and a second coil having aplurality of turns.

In accordance with yet another embodiment, a method comprises wirelesslytransferring power from a transmitting coil on a transmitter to areceiving coil on a receiver, wherein each of the transmitting coil andthe receiving coil comprises a plurality of first turns and a pluralityof second turns having a similar shape, wherein a current flowingthrough the plurality of first turns and a current flowing through theplurality of second turns are in opposite directions and communicatingbetween the transmitter and the receiver.

An advantage of a preferred embodiment of the present invention isimproving a wireless power transfer system's performance through awinding structure having better magnetic flux distribution in comparisonwith a conventional winding structure.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an implementation of a conventional coil structure;

FIG. 2 illustrates a magnetic flux distribution of the coil structureshown in FIG. 1;

FIG. 3 illustrates another magnetic flux distribution of the coilstructure shown in FIG. 1;

FIG. 4 illustrates a first implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure;

FIG. 5 illustrates a magnetic flux distribution of the coil structureshown in FIG. 4 in accordance with various embodiments of the presentdisclosure;

FIG. 6 illustrates another magnetic flux distribution of the coilstructure shown in FIG. 4 in accordance with various embodiments of thepresent disclosure;

FIG. 7 illustrates a second implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure;

FIG. 8 illustrates a third implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure;

FIG. 9 illustrates a fourth implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure;

FIG. 10 illustrates a self-canceling coil structure formed in amulti-layer PCB in accordance with various embodiments of the presentdisclosure;

FIG. 11 illustrates a coil structure including both a power transfercoil and an auxiliary coil in accordance with various embodiments of thepresent disclosure;

FIG. 12 illustrates another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure;

FIG. 13 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure;

FIG. 14 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure;

FIG. 15 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure;

FIG. 16 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure; and

FIG. 17 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely a coil structure applied in awireless power transfer system. The coil structure can improve theperformance of the wireless power transfer system. The coil structuredescribed in this disclosure can be implemented in a variety of suitablematerials and structures. For example, the winding structure may beintegrated into a substrate such as a printed circuit board (PCB), oronto a non-conducting part such as a plastic back cover of a cell phoneor a plastic case of electronic equipment. The invention may also beapplied, however, to a variety of power systems. Hereinafter, variousembodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 4 illustrates a first implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure. FIG. 4 shows a two-turn configuration of a self-cancelingcoil structure 400. The self-canceling coil structure 400 shown in FIG.4 is employed to reduce the flux expansion outside the coil structure sothat the flux density generated by the self-canceling coil structure 400decays rapidly to a lower value as the distance from the self-cancelingcoil structure 400 increases along the z-axis (a vertical direction) andalong the x-axis (a horizontal direction). The flux density of theself-canceling coil structure 400 will be described below with respectto FIGS. 5-6. Throughout the description, the self-canceling coilstructure 400 may be alternatively referred to as the coil structure 400for simplicity.

As shown in FIG. 4, a first portion 402 of the coil structure 400 startsfrom terminal 1, which is a first terminal of the coil structure 400.The end of the first portion 402 is connected to a connection element403. In some embodiments, the first portion 402 may comprise a pluralityof turns. Alternatively, the first portion 402 comprises one turn of thecoil structure 400 as shown in FIG. 4. Throughout the description, thefirst portion 402 may be alternatively referred to as the first turn402.

A starting point of a second portion 404 of the coil structure 400 isconnected to the connection element 403. The end of the second portion404 is connected to terminal 2, which is a second terminal of the coilstructure 400. In some embodiments, the second portion 404 may comprisea plurality of turns. Alternatively, the second portion 404 comprisesone turn of the coil structure 400 as shown in FIG. 4. Throughout thedescription, the second portion 404 may be alternatively referred to asthe second turn 404. As shown in FIG. 4, terminal 1 and terminal 2 areplaced immediately next to each other.

The first turn 402 and the second turn 404 shown in FIG. 4 form twoconcentric circles. As shown in FIG. 4, the second turn 404 is placednext to the first turn 402. The second turn 404 is surrounded by thefirst turn 402. More particularly, the circular portion of the secondturn 404 is enclosed by the circular portion of the first turn 402. Inaccordance with an embodiment, as shown in FIG. 4, when the currentflowing through the first turn 402 is in a clockwise direction, thecurrent flowing through the second turn 404 is in a counter-clockwisedirection.

As shown in FIG. 4, the currents flowing into the two turns 402 and 404have opposite directions, and thus the magnetic flux generated by thesecurrents tend to cancel or reduce each other outside the coil structure400. This is a self-cancellation effect of the coil structure 400. Theresulting flux density at a point away from the coil (e.g., a point awayfrom the coil structure along the Z-axis) may decay rapidly because thefluxes generated by these two currents having opposite directions maycancel each other out. At the same time, the magnetic field maystrengthen within the space between the first turn 402 and the secondturn 404. As a result, only a coil with a structure similar to the oneshown in FIG. 4 can pick up significant amount of signal or power fromthe coil structure 400 shown in FIG. 4 when the coil is placed adjacentto the coil structure 400. Such a strengthened magnetic field helps tomaintain a good coupling between the coils (e.g., coils on a transmitterand a receiver) of a wireless power transfer system, while theinterference and/or damages to nearby electronic devices and/orcomponents can be reduced or avoided.

In an embodiment, each portion (e.g., portions 402 and 404) may have oneor more turns depending on design needs. It should be noted that thefirst portion 402 and the second portion 404 may not have exactly thesame shape. As long as the first portion 402 and the second portion 404are roughly similar in shape and have a similar center location, theadvantages described above can be achieved. Furthermore, a part or theentire first portion 402 may have a different shape from the secondportion 404. The opposite directions of the currents flowing throughthese two portions may help to achieve the self-cancellation effect evenif these two portions have different shapes. However, bettercancellation can be achieved if the distance or spacing between theconductors of the two portions is uniform and well controlled. Theuniform spacing between the conductors of the two portions requiresthese two portions to have the same or a similar shape. Furthermore, theuniform spacing between the conductors of the two portions requiresthese two portions to have the same center location. Alternatively, thecenter of the first portion and the center of the second portion areadjacent to each other.

For example, a mobile phone may include a wireless power transfersystem. More particularly, the mobile phone includes a receiving coil ofthe wireless power transfer system. When a card including a near fieldcommunication (NFC) tag is placed adjacent to the mobile phone, thecoupling between the receiving coil and the NFC tag may causeinterference as well as damages to the NFC tag. This undesiredinterference and/or damages can be fixed by replacing a conventionalcoil structure with the coil structure 400 shown in FIG. 4. Inparticular, the reduced flux expansion outside the coil structure 400shown in FIG. 4 can help to reduce the coupling between the receivingcoil and the NFC tag, thereby reducing interference and/or damages tothe NFC tag.

In some embodiments, the coil structure 400 can be either used as atransmitting coil and/or a receiving coil in a wireless power transfersystem. The circular shape of the coil structure 400 may help toovercome the misalignment between the transmitting coil and thereceiving coil. For example, when both the transmitting coil and thereceiving coil are implemented as 8-shaped coils (e.g., coil 161 in FIG.11), the coupling between the transmitting coil and the receiving coilmay deteriorate when a coil rotates away from its ideal position. Incontrast, when both the transmitting coil and the receiving coil areimplemented as the coil structure 400 shown in FIG. 4, the couplingbetween the transmitting coil and the receiving coil may remainsubstantially the same when one of the two coils rotates few degreesaway from its ideal position.

FIG. 5 illustrates a magnetic flux distribution of the coil structureshown in FIG. 4 in accordance with various embodiments of the presentdisclosure. The horizontal axis of FIG. 5 represents the distance fromthe center of the circles shown in FIG. 4. The unit of the horizontalaxis is meter. The vertical axis represents the flux density of themagnetic field generated by the coil structure 400 shown in FIG. 4. Theunit of the vertical axis is Tesla. The flux density of the magneticfield is measured along the z-axis at a height of about 1 mm above thetop surface of the coil structure 400 shown in FIG. 4. The flux densityshown in FIG. 5 is taken along line B-B′ shown in FIG. 4.

FIG. 5 shows there are four positive flux density peaks 501, 504, 505and 508, and four negative flux density peaks 502, 503, 506 and 507. Inaccordance with an embodiment, the positive flux density peak 501 andthe negative flux density peak 502 are generated around the left side ofthe first turn 402 (the left intersection between the dashed line andthe first turn 402 in FIG. 4). Likewise, the negative flux density peak503 and the positive flux density peak 504 are generated around the leftside of the second turn 404 (the left intersection between the dashedline and the second turn 404 in FIG. 4).

The positive flux density peak 505 and the negative flux density peak506 are generated around the right side of the second turn 404 (theright intersection between the dashed line and the second turn 404 inFIG. 4). The negative flux density peak 507 and the positive fluxdensity peak 508 are generated around the right side of the first turn402 (the right intersection between the dashed line and the first turn402 in FIG. 4). In comparison with the flux density distribution shownin FIG. 2, the flux density distribution in FIG. 4 shows the fluxdensity is enhanced around the coil structure 400. For example, in FIG.4 a larger area within the coil structure 400 has significant fluxdensity while the flux density decays rapidly outside the coil structure400.

Referring back to FIG. 4, the two portions 402 and 404 of the coilstructure 400 are next to each other. In addition, the currents flowingthrough the two turns are in opposite directions. Slightly away from thecoil, the magnetic fields generated by the currents flowing through thetwo turns are canceled each other. As a result, the magnetic fluxdensity decays rapidly to a lower value outside a predetermined chargingarea around the coil structure 400. Such a fast decay of the magneticfield helps to reduce the impact of the coil structure 400 on theconductive components placed adjacent to the coil structure 400.

Sensitive components such as an NFC tag usually having a large coilsimilar to that shown in FIG. 1 may be placed adjacent to the coilstructure 400. As a result of having the self-cancellation effect of thecoil structure 400, the possibility of having some magnetic couplingissues such as interference, eddy current induced losses, damage tosensitive components such as an NFC IC/Tag, and the like is reduced oreliminated. The performance and reliability of a wireless power transfersystem having the coil structure 400 may be improved accordingly.

FIG. 6 illustrates another magnetic flux distribution of the coilstructure shown in FIG. 4 in accordance with various embodiments of thepresent disclosure. The horizontal axis of FIG. 6 represents thedistance from the center of the circles shown in FIG. 4. The unit of thehorizontal axis is meter. The vertical axis represents the flux densityof the magnetic field generated by the coil structure shown in FIG. 4.The unit of the vertical axis is Tesla. The flux density of the magneticfield is measured at a height of about 10 mm above the top surface ofthe coil structure shown in FIG. 4. The flux density shown in FIG. 6 istaken along line B-B′ shown in FIG. 4.

The magnetic flux distribution shown in FIG. 6 is similar to that shownin FIG. 5 except that the flux density of the magnetic field is measuredat a height of about 10 mm rather than 1 mm above the top surface of thecoil structure shown in FIG. 4.

The magnetic flux distribution shown in FIG. 6 includes two negativepeaks 602 and 602, and a negative valley 604. In comparison with theflux density shown in FIG. 3, the absolute value of the negative peaksof FIG. 6 is much lower than that shown in FIG. 3. Such a lower peakvalue helps to reduce the unnecessary coupling between the coilstructure 400 and conductive components placed adjacent to the coilstructure 400.

FIG. 7 illustrates a second implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure. FIG. 7 shows a multi-turn configuration of theself-canceling coil structure 700. Throughout the description, theself-canceling coil structure 700 may be alternatively referred to asthe coil structure 700 for simplicity.

As shown in FIG. 7, the turns of the coil structure 700 can be dividedinto two groups. A first group includes one turn 706; a second groupincludes two turns 702 and 704 placed immediately next to each other. Insome embodiments, the distance between the turn of the first group andits adjacent turn in the second group is greater than the distancebetween the two turns of the second group as shown in FIG. 7.

The three turns 702, 704 and 706 shown in FIG. 7 form three concentriccircles. The current flowing through the first group (e.g., turn 706) isin a counter-clockwise direction. In contrast, the currents flowingthrough the second group (e.g., turns 702 and 704) are in a clockwisedirection. In some embodiments, the three turns 702, 704 and 706 may beformed in a multi-layer board. For example, the turn 702 and the turn704 may be in two different layers of the multi-layer board.

It should be noted that FIG. 7 illustrates the first group having oneturn and the second group having two turns. This is merely an example.Depending on different applications and design needs, the number ofturns of each group may vary accordingly. In other words, the number ofturns in each group illustrated herein is limited solely for the purposeof clearly illustrating the inventive aspects of the variousembodiments. The present invention is not limited to any specific numberof turns.

In some embodiments, in order to achieve better magnetic coupling, avariety of parameters of the coil structure 700 may be used to improvethe performance of the coil structure 700. In accordance with anembodiment, the number of turns in the second group and/or in the firstgroup may be used as a first control variable. The distance between thefirst group and the second group may be used as a second controlvariable. By selecting appropriate values of the first control variableand the second control variable, several system performance indexes maybe improved. For example, a smooth magnetic field within a transmittercoil structure may be achieved if the coil structure 700 shown in FIG. 7is designed in the transmitter coil structure. Such a smooth magneticfield may help to improve the spatial stability of the coupling systembetween the transmitter coil and the receiver coil through maintaining astable coupling factor between the transmitter coil and itscorresponding receiver coil. In addition, by selecting the number of theturns of the second group and/or adjusting the spacing between these twogroups, the magnetic field outside the coil structure 700 could beminimized, thereby reducing the EMI problems.

FIG. 8 illustrates a third implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure. The coil structure 800 shown in FIG. 8 is similar to thecoil structure 400 shown in FIG. 4 expect that each turn is rectangularin shape. As shown in FIG. 8, a first turn 802 is rectangular in shape.The current flowing through the first turn 802 is in a counter-clockwisedirection. The second turn 804 is rectangular in shape. The second turn804 is surrounded by the first turn 802. The current flowing through thesecond turn 804 is in a clockwise direction. The advantage of having theself-canceling coil structure shown in FIG. 8 has been described abovein detail with respect to FIG. 4, and hence is not discussed again foravoiding repetition.

It should be noted that the shape of the turns in FIG. 8 are selectedpurely for demonstration purposes and are not intended to limit thevarious embodiments of the present application to any particular shape.It is within the scope of various embodiments of the present disclosurefor the turns 802 and 804 to comprise other shapes, such as, but nolimited to oval, polygon, or any other suitable shapes.

FIG. 9 illustrates a fourth implementation of a self-canceling coilstructure in accordance with various embodiments of the presentdisclosure. The coil structure 900 shown in FIG. 9 is similar to thecoil structure 400 shown in FIG. 4 expect that each turn is octagonal inshape.

As shown in FIG. 9, a first turn 902 is octagonal in shape. The currentflowing through the first turn 902 is in a counter-clockwise direction.The second turn 904 is octagonal in shape. The current flowing throughthe second turn 904 is in a clockwise direction. The second turn 904 issurrounded by the first turn 902. In addition, each side of the secondturn 904 is in parallel with a corresponding side of the first turn 902as shown in FIG. 9. The advantage of having the self-canceling coilstructure shown in FIG. 9 has been described above in detail withrespect to FIG. 4, and hence is not discussed again for avoidingrepetition.

It should be noted that the shape of the turns 902 and 904 in FIG. 9 areselected purely for demonstration purposes and are not intended to limitthe various embodiments of the present application to any particularshape. It is within the scope of various embodiments for the turns tocomprise other shapes, such as, but no limited to oval, polygon, or anyother suitable shapes.

FIG. 10 illustrates a self-canceling coil structure formed in amulti-layer PCB in accordance with various embodiments of the presentdisclosure. The self-canceling coil structure 1000 is formed in twodifferent PCB layers. As shown in FIG. 10, a top view 150 of the coilstructure 1000 shows the coil structure is formed in two different PCBlayers. At least a via (not shown) is connected between these two PCBlayers. An upper terminal 153 of the via is connected to the trace onthe first layer (shown in top view 151), and lower terminal 154 of thevia is connected to the trace of the second layer (shown in top view152).

Top views 151 and 152 show the turns of the coil structure 1000 aresplit into two portions. A first portion may be implemented as metaltraces or metal tracks on the first layer of the PCB. A second portionmay be implemented as metal traces or metal tracks on the second layerof the PCB. Furthermore, interconnect structures such as vias can beused to connect the metal traces on these two layers if necessary.

The top view 151 of the first PCB layer shows the trace of the firstlayer starts from terminal 1 and ends at the upper terminal 153 of thevia. The top view 152 of the second PCB layer shows the trace on thesecond layer starts from the lower terminal 154 of the via and ends atterminal 2.

In some embodiments, the turns shown in FIG. 10 may be a plurality ofmetal tracks/traces on a plurality layers of a printed circuit board, ora metal pattern on one or two surfaces of a non-conductive body such asa plastic back cover of a cell phone, a smart watch or other devices, ora plastic case of equipment or devices. Furthermore, the metal patternmay be printed, coated, plated or otherwise deposited onto a sidesurface or two or more side surfaces of the non-conducting body.

One advantageous feature of having the multi-layer structure shown inFIG. 10 is that the traces of these two layers may be connected inseries to provide higher inductance. On the other hand, in analternative embodiment, the traces of these two layers may be connectedin parallel to achieve lower resistance.

It should be noted that while the turns shown in FIG. 10 aresubstantially rectangular in shape, it is within the scope and spirit ofthe invention for the turns to comprise other shapes, such as, but notlimited to oval, square, or circular. It should further be noted thatwhile FIG. 10 illustrates each layer with four turns, the coil structure1000 could accommodate any number of turns.

As the communication between transmitters and receivers has become animportant requirement for designing a reliable and efficient wirelesspower transfer system having various features such as power control,status reporting, device authentication, advertisements and othersuitable information exchanges, a variety of communication mechanismshave been adopted in the wireless power transfer system. One method isusing Bluetooth (a wireless technology standard for exchanging data overshort distances) as a communication link between a transmitter and areceiver of the wireless power transfer system. However, the Bluetoothcircuit is relatively expensive. In addition, there may be a startupissue for the Bluetooth circuit on the receiver side if the power of thereceiver side has been completely drained.

In some systems, an in-band communication technique can be employed tofulfill the communication between transmitters and receivers. Moreparticularly, the signal of the in-band communication can be detected bythe transmitter side by modulating the load or other circuit oroperating parameters on the receiver side. The transmitter detects thesignal and converts it into a corresponding digital signal. Similarly, amodulation of a circuit or operating parameter in a transmitter may beused to communicate a signal from the transmitter to one or morereceivers coupled to the transmitter. In some embodiments, themodulation of the circuit or operating parameter means intentionallychanging the circuit or operating parameter in a predetermined manner.The cost of implementing the in-band communication is relatively low.However, the accuracy of the in-band communication technique issensitive to the load variations and other operation variations in thewireless power transfer system. In addition to the in-band communicationthrough the power transfer coils in a wireless power transfer system, amore reliable communication channel can be established through adedicated auxiliary coil which has lower interference with the powertransfer coils.

FIG. 11 illustrates a coil structure including both a power transfercoil and an auxiliary coil in accordance with various embodiments of thepresent disclosure. FIG. 11 shows an auxiliary coil 161 and a wirelesspower transfer coil 162 are integrated in one coil structure 1100. Asshown in FIG. 11, the auxiliary coil 161 is slightly bigger than thepower transfer coil 162. In some embodiments, the auxiliary coil 161 maybe a bias coil for supplying a bias voltage and/or a communication coilfor providing a high speed, bi-directional communication link in awireless power transfer system.

In alternative embodiments, the auxiliary coil 161 may be another powertransfer coil providing power in a different path, a different frequencyand/or a different power transfer standard in comparison with the mainpower transfer coil 162. In some embodiments, the auxiliary coil 161 maytransfer both power and communication signals through a same in-bandcommunication channel. The main power transfer coil 162 and theauxiliary coil 161 may operate simultaneously.

Furthermore, when the main power transfer coil 162 and the auxiliarycoil 161 operate simultaneously, either one can be a receiver coil or atransmitter coil. In other words, it is possible to configure one coilof FIG. 11 to be a transmitter coil and the other to be a receiver coilwhen they operate simultaneously. Alternatively, both coils of FIG. 11may function as transmitter coils coupled to their respective receivercoils (not shown). Furthermore, both coils of FIG. 11 may function asreceiver coils coupled to their respective transmitter coils (notshown). In order to eliminate or reduce the magnetic interferencebetween these two coils of FIG. 11, at least one of the coils 161 and162 should have a self-cancellation magnetic structure.

In accordance with an embodiment, the auxiliary coil 161 is implementedas a communication coil. Throughout the description, the auxiliary coil161 is alternatively referred to as the communication coil 161.

The communication coil 161 shown in FIG. 11 is coupled to acommunication circuit (not shown) which can generate a plurality ofvoltage or current pulses suitable for communication purposes. As shownin FIG. 11, the power transfer coil 162 is implemented as a conventionalmulti-turn coil. More particularly, the power transfer coil 162 has twoturns starting from terminal T1 and ending at terminal T2 as shown inFIG. 11. The flux generated by the power transfer coil 162 is basicallyunidirectional in the area enclosed by a communication coil 161.

The communication coil 161 may be implemented as a self-cancellingstructure such as the coil structures shown in FIGS. 4 and 7-10.Alternatively, the communication coil 161 may be an 8-shaped structureas shown in FIG. 11. The communication coil 161 has a self-enclosedmagnetic path. As shown in FIG. 11, the communication coil 161 isdivided into two portions, namely a first portion 352 and a secondportion 354. Each portion comprises a straight line and an arc. Thestraight line of the first portion 352 and the straight line of thesecond portion 354 are placed adjacent to each other, thereby enhancingthe magnetic flux distribution of the communication coil 161. The arc ofeach portion connects the two terminals of the straight line with arelatively short length for a given area. Such a relatively short lengthhelps to reduce the resistance of the communication coil 161.

As shown in FIG. 11, the first portion 352 forms a first half circle.Likewise, the second portion 354 forms a second half circle. When acurrent flows through the communication coil 161, each portion of thewinding will generate a magnetic flux. The direction of the magneticflux in the first half circle is opposite to the direction of themagnetic flux in the second half circle with reference to the verticalaxis which is perpendicular to the winding. The magnetic fluxes inopposite directions form a self-enclosed magnetic path. Such aself-enclosed magnetic path helps to enhance the magnetic field withinthese two portions 352 and 354, and reduce the magnetic flux outside thecommunication coil 161 through a self-cancellation effect.

With the coil arrangement shown in FIG. 11, the magnetic field generatedby the power transfer coil 162 generates a very low voltage(approximately equal to zero) across two terminals T3 and T4 of thecommunication coil 161. At the same time, the magnetic field generatedby the communication coil 161 generates a very low voltage(approximately equal to zero) across two terminals T1 and T2 of thepower transfer coil 162. Such low voltages (e.g., voltage across T3 andT4, and voltage across T1 and T2) help to eliminate or reduce theinterference or damages to coils and/or circuits coupled to the coilsshown in FIG. 11.

In some embodiments, the communication coil 161 is so arranged such thatthe magnetic fluxes coupled to both the first portion 352 and the secondportion 354 can form a closed loop within the space immediately adjacentto the communication coil 161, and the current in each portion of thecommunication coil 161 strengthens this coupled flux. In contrast, to apoint outside this space, the magnetic flux there has been weakenedbecause the magnetic flux from the first portion 352 and the magneticflux from the second portion 354 tend to cancel each other out.

It should be noted that the communication coil 161 may be formed in atleast two different layers of a PCB. In an embodiment, the communicationcoil 161 may be formed in two PCB layers immediately next to each other.Alternatively, the PCB layers where the communication coil 161 is formedmay be separated by other PCB layers. Furthermore, the communicationcoil 161 and the power transfer coil 162 may be formed in differentlayers of the PCB.

In the communication coil 161, the 8-shaped structure helps to enhancethe magnetic field within these two portions 352 and 354 and reduce themagnetic flux outside the communication coil 161. As a result, thecommunication signal from the other communication coil coupled to thecommunication coil 161 can generate a strong coupling to a nearby coilwith a similar structure, thereby producing a strong signal or a largeamount of power transfer to the nearby coil.

FIG. 12 illustrates another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1200 shown inFIG. 12 is similar to the coil structure 1100 shown in FIG. 11 exceptthat the power transfer coil 163 has three turns and the communicationcoil 164 is smaller than the power transfer coil 163, and thecommunication coil 164 is located inside and surrounded by the powertransfer coil 163. In some embodiments, the power transfer coil 163 andthe communication coil 164 may be formed in two different layers of aPCB.

One advantageous feature of having the coil structure 1200 shown in FIG.12 is the 8-shaped structure of the communication coil 164 is aself-cancellation magnetic structure. As a result, the interferencebetween the communication coil 164 and the power transfer coil 163 hasbeen minimized.

FIG. 13 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1300 shown inFIG. 13 is similar to the coil structure 1100 shown in FIG. 11 exceptthat the power transfer coil 172 has an 8-shaped structure. In someembodiments, the 8-shaped structure may be formed in two differentlayers of a PCB. The operation and the advantage of the 8-shapedstructure have been described above with respect to FIG. 11, and henceare discussed again to avoid repetition.

It should be noted the 8-shaped structure is merely an example. A personskilled in the art would understand there may be variations,modifications and alternatives. For example, the power transfer coil 172can be other suitable coil structures such as the self-cancelling coilsshown in FIGS. 4 and 7-10.

As shown in FIG. 13, the communication coil 171 has one turn, which canbe implemented as a coil circular in shape. Alternatively, thecommunication coil 171 can other suitable coils such as a race trackcoil, a round coil or a rectangular coil. The communication coil 171 canbe placed in a transmitter and/or a receiver coupled to the transmitter.In some embodiments, the communication coil 171 is independentlycontrolled. As such, the communication coil 171 does not rely on thewireless power transfer system to transfer communication signals.Therefore, the communication based upon the coil structure shown in FIG.13 is immune to load variations and other transients in the wirelesspower transfer system. The communication coil 171 is able to transferbi-directional signals. Such a bi-directional communication system cangreatly improve the wireless power transfer system's performance byproviding a negotiation path between the transmitter and the receiver ofthe wireless power transfer system.

FIG. 14 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1400 shown inFIG. 14 is similar to the coil structure 1300 shown in FIG. 13 exceptthat the diameter of the power transfer coil 173 is greater than thediameter of the communication coil 174. More particularly, thecommunication coil 174 is surrounded by the power transfer coil 173. Itshould be noted that, in some embodiments, the power transfer coil 173and the communication coil 174 may be formed in two different layers ofa PCB.

FIG. 15 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1500 shown inFIG. 15 is similar to the coil structure 1300 shown in FIG. 13 exceptthat the power transfer coil 182 has a structure similar to that shownin FIG. 4. It should be noted that while the diameter of the auxiliarycoil 181 is greater than the diameter of the power transfer coil 182,the diameter of the power transfer coil 182 may be greater than thediameter of the auxiliary coil 181 depending on different applicationsand design needs.

FIG. 16 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1600 shown inFIG. 16 is similar to the coil structure 1500 shown in FIG. 15 exceptthat the auxiliary coil 183 has a structure similar to that shown inFIG. 4.

It should be noted that while FIG. 16 illustrates the power transfercoil 184 is surrounded by the auxiliary coil 183, depending on differentapplications and design needs, the auxiliary coil 183 may be placed inthe area surrounded by the power transfer coil 184.

FIG. 17 illustrates yet another coil structure including both a powertransfer coil and an auxiliary coil in accordance with variousembodiments of the present disclosure. The coil structure 1700 shown inFIG. 17 is similar to the coil structure 1600 shown in FIG. 16 exceptthat the power transfer coil 186 has a conventional one turn structure.

It should be noted that the power transfer coil 186 can be placed eitherinside the auxiliary coil 185 as shown in FIG. 17 or outside theauxiliary coil 185 depending on different applications and design needs.

Although embodiments of the present invention and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A structure comprising: a plurality of firstturns of a coil; and a plurality of second turns of the coil having asimilar shape as the plurality of first turns of the coil, wherein: theplurality of first turns of the coil and the plurality of second turnsof the coil have a similar center position; and a current flowingthrough the plurality of first turns of the coil and a current flowingthrough the plurality of second turns of the coil are in oppositedirections.
 2. The structure of claim 1, wherein: the plurality of firstturns of the coil is circular in shape.
 3. The structure of claim 2,wherein: the plurality of first turns of the coil starts from a firstterminal of the coil and ends at a connection element; and the pluralityof second turns of the coil starts from the connection element and endsat a second terminal of the coil, and wherein: the plurality of secondturns of the coil is surrounded by the plurality of first turns of thecoil; and the first terminal and the second terminal are placedimmediately next to each other.
 4. The structure of claim 1, wherein: aturn in the plurality of first turns of the coil has a slightlydifferent shape from a turn in the plurality of second turns of thecoil.
 5. The structure of claim 1, wherein: the plurality of first turnsof the coil is rectangular in shape.
 6. The structure of claim 1,wherein: the plurality of first turns of the coil is octagonal in shape.7. The structure of claim 1, further comprising: a plurality of thirdturns of the coil and a plurality of fourth turns of the coil, wherein:the plurality of third turns of the coil and the plurality of fourthturns of the coil have a similar shape and a similar center position;and a current flowing through the plurality of third turns of the coiland a current flowing through the plurality of fourth turns of the coilare in opposite directions.
 8. The structure of claim 7, wherein: theplurality of first turns of the coil and the plurality of second turnsof the coil are placed on a first layer of a printed circuit board; andthe plurality of third turns of the coil and the plurality of fourthturns of the coil are placed on a second layer of the printed circuitboard.
 9. The structure of claim 8, further comprising: a via in theprinted circuit board and connected between the plurality of secondturns of the coil and the plurality of third turns of the coil.
 10. Asystem comprising: a first coil having a first winding structurecomprising: a plurality of first turns and a plurality of second turnsof the first coil having a similar shape, wherein: the plurality offirst turns and the plurality of second turns have a similar centerposition; and a current flowing through the plurality of first turns anda current flowing through the plurality of second turns are in oppositedirections; and a second coil having a plurality of turns.
 11. Thesystem of claim 10, wherein: the first coil is placed inside the secondcoil.
 12. The system of claim 10, wherein: the first coil is placedoutside the second coil.
 13. The system of claim 10, wherein: one of thefirst coil and the second coil is configured to transfer power.
 14. Thesystem of claim 10, wherein: one of the first coil and the second coilis configured to transfer communication signals.
 15. The system of claim10, wherein: one of the first coil and the second coil is configured totransfer both power and communication signals.
 16. A method comprising:wirelessly transferring power from a transmitting coil on a transmitterto a receiving coil on a receiver, wherein each of the transmitting coiland the receiving coil comprises: a plurality of first turns and aplurality of second turns having a similar shape, and wherein a currentflowing through the plurality of first turns and a current flowingthrough the plurality of second turns are in opposite directions; andcommunicating between the transmitter and the receiver.
 17. The methodof claim 16, wherein: the step of communicating between the transmitterand the receiver is achieved by modulating a circuit parameter or anoperation parameter of the transmitter.
 18. The method of claim 17,wherein: the communicating between the transmitter and the receiver isthrough a communication coil placed at the transmitter.
 19. The methodof claim 16, wherein: the step of communicating between the transmitterand the receiver is achieved by modulating a circuit parameter or anoperation parameter of the receiver.
 20. The method of claim 19,wherein: the communicating between the transmitter and the receiver isthrough a communication coil placed at the receiver.